Whirlpool AKZ164 Oven

Hi All.
A customer has a problem with their Whirlpool AKZ164 built in oven.
It is a model which incorporates the self-cleaning pyrolytic facility.
The problem that they have is this, they went away on holiday for a fortnight, and like good people turned the oven off at the wall.
When they came back they switched the oven back on and soon after setting the clock a red padlock symbol started to flash continuously.
The oven will still work and the temperature is regulated correctly.
The oven door switch, the one that operates the light and fan relay(s) is working fine.
We tried to get the oven to go into a clean or express clean program but it wouldn’t start that process.
Does anybody have any idea what might have failed or gone wrong?

Many thanks
Dave